1. Field of Invention
The invention relates to personal security systems for emitting and locating emergency radio-frequency transmissions, and more specifically to such systems including features for monitoring security routes such as guard tours.
2. Description of the Prior Art
Personal security systems of the type most pertinent to the present invention include portable radio-frequency transmitters carried by a system subscriber for actuation in emergency or threatening situations. Fixed receivers monitor the area where the system is installed and initiate a planned sequence of events when an emergency transmission is detected. Sirens and strobes may be energized to scare away attackers, and appropriate security personnel may be called to provide assistance. The system usually is monitored from a control station having a program that uses the known positions of the signal-detecting receivers to identify the approximate location of the threatened subscriber. Examples are disclosed in Shields U.S. Pat. No. 4,998,095, issued Mar. 5, 1991; DeMarco U.S. Pat. No. 4,764,757, issued Aug. 16, 1988; and Levinson U.S. Pat. No. 4,611,198, issued Sep. 9, 1986. An improved approach for more precisely locating the transmission is disclosed in Kostusiak et al. U.S. Pat. No. 5,115,224, issued May 19, 1992. In addition to the known positions of the monitoring receivers, Kostusiak et al. use the relative strengths of the signals compared between several receivers.
Personal security systems that include guard tour features are not common. Some examples exist where private branch exchanges (PBX), including many different types of communications devices, are provided with features for use by security personnel. Vanacore U.S. Pat. No. 4,672,654, issued Jun. 9, 1987, is one such example that discloses a PBX system with algorithms for monitoring guard tours.